Main bearing for crankshaft of internal combustion engine

ABSTRACT

A main bearing includes first and second half bearings, each having a main cylinder portion and crush relief portions in both circumferential end portions. An oil groove circumferentially extends on an inner circumferential surface only of the first half bearing, one circumferential end portion of the oil groove opens on a circumferential end surface on a front side in a rotation direction, and the other circumferential end portion of the oil groove is positioned in the main cylinder portion. The first half bearing includes a transition region at least between the crush relief portion on the rear side in the rotation direction and the main cylinder portion, and the second half bearing includes a transition region at least between the crush relief portion on the front side in the rotation direction and the main cylinder portion.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention of the present application relates to a main bearing forsupporting a crankshaft of an internal combustion engine.

(2) Description of Related Art

A crankshaft of an internal combustion engine is supported at a journalsection thereof by a cylinder block lower part of the internalcombustion engine via a main bearing made of a pair of half bearings.For the main bearing, a lubricating oil that is discharged by an oilpump is fed into a lubricating oil groove that is formed along an innercircumferential surface of the main bearing through a through-port thatis formed in a wall of the main bearing from an oil gallery that isformed in a cylinder block wall. Further, a first lubricating oil pathis formed by being penetrated in a diameter direction of the journalsection, and both end openings of the first lubricating oil pathcommunicate with the lubricating oil groove of the main bearing.Furthermore, a second lubricating oil path passing through a crank armsection is formed by branching from the first lubricating oil path inthe journal section, and the second lubricating oil path communicateswith a third lubricating oil path that is formed by being penetrated ina diameter direction of a crankpin. In this manner, the lubricating oilwhich is fed into the lubricating oil groove formed on the innercircumferential surface of the main bearing through the through-portfrom the oil gallery in the cylinder block wall passes through the firstlubricating oil path, the second lubricating oil path and the thirdlubricating oil path, and is supplied between a sliding surface of thecrankpin and a connecting rod bearing from a discharge port that isopened in a terminal end of the third lubricating oil path (for example,see JP-A-8-277831).

Conventionally, as the main bearing and the connecting rod bearing,sliding bearings each configured by a pair of half bearings have beenadopted, and in each of the sliding bearings, a so-called crush reliefis formed adjacently to abutment surfaces of the half bearings. A crushrelief corresponds to a gap region that is formed in a space from ashaft to be supported by forming a wall thickness of a region adjacentto a circumferential end surface of a half bearing so that the wallthickness becomes thinner toward the circumferential end surface (forexample, see SAE J506 (item 3.26 and item 6.4), DIN1497 (section 3.2),JIS D3102). The crush relief is formed with an objective of absorbing apositional displacement and deformation of the butting surfaces of thehalf bearings in a state in which a pair of half bearings are assembled(For example, see JP-A-4-219521).

Meanwhile, in recent years, in order to decrease the leakage amount ofthe lubricating oil from a bearing end portion in response to downsizingof a lubricating oil supplying oil pump, there are proposed a bearing inwhich a circumferential groove is formed by boring an innercircumferential surface of a bearing circumferential end portion, or abearing which is configured so as not to communicate a lubricating oilgroove formed along an inner circumferential surface of the bearing witha crush relief (namely, configured to form a raised portion between thelubricating oil groove and the crush relief) (see JP-A-2011-58568, andJP-A-2008-95858).

SUMMARY OF THE INVENTION

Here, an operation of the prior art in which a circumferential endportion, on a rear side in a rotation direction of a crankshaft, of anoil groove 141 a formed along an inner circumferential surface of a halfbearing 141 is not communicated with a crush relief 170U on the rearside in the rotation direction of the crankshaft will be described withuse of FIGS. 15A and 15B, and FIGS. 16A and 16B. As described above,when an inlet opening 6 c for a lubricating oil path 6 a on the surfaceof a journal section 6 is located at a main cylinder surface 171 of alower half bearing 142, a gap between the surface of the journal section6 and the main cylinder surface 171 of the half bearing 142 is narrow.Therefore, the inlet opening 6 c is closed by the main cylinder surface171 of the half bearing 142, and by the influence of a centrifugal forceby rotation of the crankshaft, the pressure of the lubricating oil inthe vicinity of the inlet opening 6 c in the lubricating oil path 6 a isin an extremely high state.

As shown in FIGS. 16A and 16B, at the moment when the inlet opening 6 cfor the lubricating oil path 6 a in the surface of the journal section 6and the crush relief 170L start communication, an jet flow (back-flow)of the oil to a relief gap side from the lubricating oil path 6 a isinstantaneously and temporarily formed due to the difference between thepressure of the lubricating oil inside the lubricating oil path 6 a, andthe pressure of the lubricating oil in the gap (the relief gap) betweenthe crush relief 170L and the surface of the journal section 6.

On that occasion, the jet flow mainly flows into only crush reliefgrooves 175 that communicate with the inlet opening 6 c for thelubricating oil path 6 a, because the relief gap in the region of thecircumferential end portion of the crush relief 170L is narrow.Therefore, the jet flow of the lubricating oil is extremely strong.

Subsequently, the jet flow of the high-pressure oil that flows into thecrush relief grooves 175 moves straight ahead in the crush reliefgrooves 175, passes over an axial groove 176 by an inertia force, and isconcentratedly fed into a relief gap of the other half bearing 141 whileremaining in a high-pressure state.

In that case, when the jet flow of the high-pressure oil reaches avicinity of a circumferential end portion of the crush relief 170U ofthe other half bearing 141 (namely, an end portion of the crush reliefon a central portion side in the circumferential direction of the halfbearing 141) as shown in FIGS. 16A and 16B, the pressure of the oilrapidly reduces, and therefore a vacancy (a bubble) 200 is easilygenerated in the oil. More specifically, the reason why the pressure ofthe oil reduces is that all of the high-pressure oil can not enter anarrow region in the relief gap or a further narrow region ahead of itbetween the main cylinder surface and the journal surface, and thereforethe flow of the oil is disturbed (becomes a disturbed flow).

Generation spots of the vacancies (the bubbles) concentrate in a regionin the vicinity of the circumferential end portion of the crush relief170U on the rear side in the rotation direction of the crankshaft of thehalf bearing 141, over which region the inlet opening 6 c of thelubricating oil path 6 a on the surface of the journal section 6 passes,and therefore, rupture, and collapse of the vacancies (the bubbles)concentratedly occur in the region. Due to the impact thereof,cavitation erosion easily occurs at the inner circumferential surface ofthe crush relief 170U of the half bearing 141.

An object of the invention of the present application is to provide amain bearing for a crankshaft of an internal combustion engine that isexcellent in restraining cavitation erosion.

In order to attain the above described object, according to one aspectof the invention of the present application, there is provided:

a main bearing for rotatably supporting a journal section of acrankshaft of an internal combustion engine, the journal sectioncomprising a cylindrical body part, a lubricating oil path extending topenetrate the cylindrical body part, and two inlet openings of thelubricating oil path that are formed on an outer circumferential surfaceof the cylindrical body part, wherein

the main bearing comprises first and second half bearings which arecombined into a cylindrical shape by butting respective circumferentialend surfaces,

the first and second half bearings are configured to form an axialgroove extending through an entire length of the main bearing in anaxial direction on an inner circumferential surface side of each buttingportion when the first and second half bearings are combined,

each half bearing has a main cylinder portion including a centralportion of the half bearing in the circumferential direction, and crushrelief portions which are formed throughout an entire length of the halfbearing in the axial direction at both end portions of the half bearingin the circumferential direction so that a wall thickness of the crushrelief portion becomes thinner than that of the main cylinder portion,each crush relief portion extending from the end surface of the halfbearing in the circumferential direction toward the central portion inthe circumferential direction with a center angle not less than 3° andnot more than 15°,

a plurality of crush relief grooves extending in the circumferentialdirection through an entire length of the crush relief portion areformed in each crush relief portion to communicate with the axialgroove,

an oil groove is formed only on an inner circumferential surface of thefirst one of the first and second half bearings to extend in thecircumferential direction, a circumferential end portion of the oilgroove on a front side of a rotation direction of the crankshaft openingon the circumferential end surface of the first half bearing on thefront side of the rotation direction, a circumferential end portion ofthe oil groove on a rear side of the rotation direction of thecrankshaft being positioned in the main cylinder portions of the firsthalf bearing,

the first half bearing further has a transition region formed at leastbetween the crush relief portion on a rear side in the rotationdirection of the crankshaft and the main cylinder portion in such amanner that a wall thickness of the transition region becomes thinnertoward the crush relief portion from the main cylinder portion,

the second half bearing further has a transition region formed at leastbetween the crush relief portion on a front side in the rotationdirection of the crankshaft and the main cylinder portion in such amanner that a wall thickness of the transition region becomes thinnertoward the crush relief portion from the main cylinder portion, and

the transition region comprises an inward protruding curved surface in aprotruding shape which protrudes inward in a radial direction, seen fromthe axial direction of the half bearing.

In the above described main bearing, each crush relief portionconnecting to the transition region preferably has a depth of 0.002 mmto 0.030 mm in a radial direction in the connecting position.

Further, in the above described main bearing, each transition regionpreferably has a length of 1 mm to 4 mm in the circumferentialdirection.

Further, in the above described main bearing, each crush relief groovepreferably has a depth of 1 μm to 20 μm in the radial direction, and awidth of 0.05 mm to 0.5 mm in the axial direction.

Further, in the above described main bearing, when the first and secondhalf bearings are combined, the respective crush relief grooves whichare formed in the crush relief portions of the first half bearings arepreferably adapted to be displaced in the axial direction with respectto the respective crush relief grooves which are formed in the crushrelief portions of the second half bearing by an amount exceeding zeroat a minimum and less than the width of the crush relief groove at amaximum.

Further, in the above described main bearing, each axial groovepreferably has a depth of 0.1 mm to 1 mm in the radial direction, and awidth of 0.3 mm to 2.0 mm in the circumferential direction.

Further, in the above described main bearing, each transition region mayhave the inward protruding curved surface on a side far from theadjacent crush relief portion, and may have an outward protruding curvedsurface in a protruding shape protruding outward in the radial directionon a side near to the crush relief portion.

Further, in the above described main bearing, the depth of the oilgroove may be maximum at the circumferential end surface of the firsthalf bearing on the front side of the rotation direction of thecrankshaft, and may become smaller toward the circumferential endportion of the oil groove on the rear side of the rotation direction.

As shown in FIGS. 13A and 13B, in the invention of the presentapplication, an inlet opening 6 c is closed by a main cylinder surface71 of a half bearing 42 while the inlet opening 6 c for the lubricatingoil in the surface of the journal section 6 is located at the maincylinder surface 71 (the inner surface of the main cylinder portion) ofthe half bearing 42, but since the lubricating oil in a lubricating oilpath 6 a is pressed toward the inlet opening 6 c side by the centrifugalforce by rotation of the crankshaft, the pressure of the lubricating oilin the vicinity of the inlet opening 6 c in the lubricating oil path 6 ais in an extremely high state, especially when the rotational speed ofthe crankshaft is high in an operation of the internal combustionengine.

However, as shown in FIGS. 14A and 14B, at the moment when the inletopening 6 c of the lubricating oil path 6 a in the surface of thejournal section 6 and the transition region 73 start communication, thehigh-pressure lubricating oil that instantaneously jets and flowsbackward into the relief gap from the lubricating oil path 6 a dispersesand flows into the relief gap due to the difference between the pressureof the lubricating oil inside the lubricating oil path 6 a and thepressure of the lubricating oil in a gap (a relief gap) among a crushrelief portion 70, a transition region 73 and the surface of the journalsection 6. Since the half bearing 42 of the invention of the presentapplication has the transition region 73, the jet flow of thehigh-pressure lubricating oil disperses and flows in the bearing widthdirection of the relief gap.

When the lubricating oil which has a high pressure in the lubricatingoil path 6 a flows into the relief gap (the gap between the surface ofthe crush relief portion and the surface of the journal section) of thehalf bearing 42, the pressure of the lubricating oil reduces, and acavitation phenomenon in which vacancies (bubbles) 200 are generated inthe lubricating oil sometimes occurs.

In the invention of the present application, the lubricating oil thathas a high pressure disperses and flows into the relief gap of the halfbearing 42, and therefore, generation of vacancies (bubbles) dispersesin the relief gap of the half bearing 42 on the lower side.

When the vacancies (bubbles) generated in the lubricating oil raptureand collapse, a force (an impact force) occurs, and if the spots wherevacancies (bubbles) rapture and collapse concentrate in a particularsite in the relief gap of the half bearing 42, the surface of the crushrelief portion of the half bearing 42 is sometimes damaged (cavitationerosion).

In the invention of the present application, the generation spots ofvacancies (bubbles) disperse in the relief gap as described above, andthe spots where the vacancies (the bubbles) rapture also disperse in therelief gap. Therefore, in the crush relief surface of the half bearing42, cavitation erosion hardly occurs.

Further, the vacancies (the bubbles) that do not collapse in the reliefgap of the half bearing 42 are guided to the crush relief grooves 75together with the lubricating oil, are fed to the axial groove 77, andare further discharged to an outside from both the end portions in thebearing width direction of the axial groove 77 together with thelubricating oil.

Accordingly, in the half bearing 42 of the invention, the lubricatingoil which has been under high pressure in the lubricating oil path isnot forwarded in a concentrated manner to a region near an end portionof the relief gap on the central portion side in the circumferentialdirection of the other half bearing 41, over which region the inletopening 6 c of the lubricating oil path 6 a on the surface of thejournal section 6 passes. Further, since the volume in the region nearthe end portion of the relief gap on the central portion side in thecircumferential direction of the half bearing 41 becomes larger thanthat of a conventional bearing, an impact force generated when thevacancies (bubbles) collapses is relieved, and therefore the problemhardly arises that cavitation erosion occurs in an inner circumferentialsurface of the crush relieve portion 70 of the half bearing 41.

Further, according to the invention of the present application, theformation range of the crush relief portion is from 3° to 15° inclusiveas the circumferential angle (θ) starting from the circumferential endsurface of the half bearing. The reason thereof is that if the formationrange of the crush relief is from the circumferential end surface of thehalf bearing to less than 3° in the circumferential angle (θ), thecapacity of the relief gap is so small that the oil flowing out of theinlet opening 6 c hardly disperses and flows out to the relief gap,whereas if the circumferential angle (θ) exceeds 15°, oil includingvacancies (bubbles) passes over the axial groove 77 and easily advancesinto the inner circumferential surface of the other half bearing, andthe leakage amount of the oil to the outside from the half bearings 41and 42 also increases.

In more detail, oil flows (oil flows shown by the arrows) that flow intothe relief gap from the transition region 73 in FIG. 14A collide with anoil flow that flows to the relief gap from a gap side between the maincylinder portion and the journal surface not illustrated, accompaniesthe journal surface and moves straight ahead in the circumferentialdirection of the bearing in such a manner as to intersect one another inthe relief gap. Therefore, in the relief gap, the flow of the oil whichflows in the circumferential direction of the bearing is weakened. Ifthe formation range of the crush relief exceeds 15° in thecircumferential angle (θ), in the vicinity of the circumferential endportion of the half bearing in the relief gap, the oil which isdecreased in the speed of straight movement in the circumferentialdirection at the upstream side of the relief gap increases in the speedof straight movement in the circumferential direction of the bearingagain, until the oil accompanies the journal surface and is fed to thevicinity of the circumferential end portion of the half bearing in therelief gap, whereby the oil including vacancies (bubbles) passes overthe axial groove and easily advances into the inner circumferentialsurface of the other half bearing.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a sectional view of a crankshaft of an internal combustionengine cut at a journal section and a crankpin section;

FIG. 2 is a front view of one half bearing according to an embodiment ofthe invention of the present application;

FIG. 3 is a bottom view of the one half bearing according to theembodiment of the invention of the present application;

FIG. 4 is a bottom view of the other half bearing according to theembodiment of the invention of the present application;

FIG. 5 is a front view of a main bearing in a state in which a pair ofhalf bearings is assembled;

FIG. 6 is an enlarged front view explaining a shape in a vicinity of acrush relief;

FIG. 7 is a development explaining specific dimensions by developing amain cylinder portion in a planar fashion in regard with the shape inthe vicinity of the crush relief;

FIG. 8 is a sectional view of crush relief grooves;

FIG. 9 is a sectional view of an axial groove;

FIG. 10 is an explanatory view explaining positional relationshipbetween paired crush relief grooves;

FIG. 11 is a front view of one half bearing according to anotherembodiment of the invention of the present application;

FIG. 12 is a view seen from a bearing inner side for explaining a pairof half bearings according to another embodiment of the invention of thepresent application;

FIG. 13A is a view seen from the bearing inner side for explaining anoperation of a main bearing of the invention of the present application;

FIG. 13B is a front view for explaining the operation of the mainbearing of the invention of the present application;

FIG. 14A is a view seen from the bearing inner side for explaining theoperation of the main bearing of the invention of the presentapplication;

FIG. 14B is a front view for explaining the operation of the mainbearing of the invention of the present application;

FIG. 15A is a view seen from a bearing inner side for explaining anoperation of a main bearing of a prior art;

FIG. 15B is a front view explaining the operation of the main bearing ofthe prior art;

FIG. 16A is a view seen from the bearing inner side for explaining theoperation of the main bearing of the prior art; and

FIG. 16B is a front view explaining the operation of the main bearing ofthe prior art.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention of the present applicationwill be described with reference to the drawing. Note that in order tofacilitate the understanding of the embodiments, crush reliefs areillustrated by being emphasized in the drawing.

(Entire Configuration of Bearing Device)

As shown in FIG. 1, a bearing device 1 of each of the presentembodiments includes a journal section 6 that is supported by a lowerpart of a cylinder block 8, a crankpin 5 that is formed integrally withthe journal section 6 and revolves around the journal section 6, and aconnecting rod 2 that transmits reciprocal movement from an internalcombustion engine to the crankpin 5. The bearing device 1 furtherincludes a main bearing 4 that rotatably supports the journal section 6,and a connecting rod bearing 3 that rotatably supports the crankpin 5,as sliding bearings that support a crankshaft.

Note that while the crankshaft has a plurality of journal sections 6 anda plurality of crankpins 5, explanation will be made by illustrating oneof the journal sections 6 and one of the crankpins 5 here forconvenience of explanation. In FIG. 1, positional relation in a depthdirection of the page is such that the journal section 6 is on a backside of the page, and the crankpin 5 is on a front side thereof.

The journal section 6 is pivotally supported by a cylinder block lowerpart 81 of an internal combustion engine via the main bearing 4 that isconfigured by a pair of half bearings 41 and 42. In the half bearing 41which is on an upper side in FIG. 1, an oil groove 41 a is formed on aninner circumferential surface in a circumferential direction. Further,the journal section 6 has a lubricating oil path 6 a that penetrates inthe diameter direction, and when the journal section 6 rotates in anarrow X direction, inlet openings 6 c at both ends of the lubricatingoil path 6 a alternately communicate with the oil groove 41 a of themain bearing 4.

The crankpin 5 is pivotally supported by a large end portion housing 21(a rod side large end portion housing 22 and a cap side large endportion housing 23) of the connecting rod 2 via the connecting rodbearing 3 which is configured by a pair of half bearings 31 and 32.

As described above, for the main bearing 4, a lubricating oil that isdischarged by an oil pump is fed into the oil groove 41 a which isformed along the inner circumferential surface of the main bearing 4through a through-port formed in a wall of the main bearing 4 from anoil gallery formed in a cylinder block wall.

Furthermore, the first lubricating oil path 6 a is formed to penetratein the diameter direction of the journal section 6, and the inletopening 6 c of the first lubricating oil path 6 a communicates with thelubricating oil groove 41 a. A second lubricating oil path 5 a thatbranches from the first lubricating oil path 6 a of the journal section6 and passes through a crank arm section (not illustrated) is formed,and the second lubricating oil path 5 a communicates with a thirdlubricating oil path 5 b that is formed to penetrate in a diameterdirection of the crankpin 5.

In this manner, the lubricating oil passes through the first lubricatingoil path 6 a, the second lubricating oil path 5 a and the thirdlubricating oil path 5 b, and is supplied to a gap that is formedbetween the crankpin 5 and the connecting rod bearing 3, from adischarge port 5 c at an end portion of the third lubricating oil path 5b.

(Configuration of Half Bearing)

The main bearing 4 of the present embodiment is formed by butting endsurfaces in a circumferential direction of the pair of half bearings 41and 42, and assembling the pair of half bearings 41 and 42 into acylindrical shape as a whole (see FIG. 5). Each half bearing 41 (or 42)is formed into a semi-cylindrical shape by a bimetal formed by bonding abearing alloy thinly on a steel plate as shown in FIG. 2. The halfbearing 41 includes a main cylinder portion 71 that is formed byincluding a central portion in a circumferential direction, crush reliefportions 70 and 70 that are formed at both end portions in thecircumferential direction, and transition regions 73 and 73 that arelocated between the main cylinder portion 71 and the crush reliefportions 70 and 70, and are formed in such a manner that wallthicknesses thereof become thinner toward the crush relief portions 70and 70.

Embodiment 1

As is understood from FIGS. 3 and 5, the oil groove 41 a which is formedon the inner circumferential surface of the half bearing 41 is formed toextend through the central portion in the circumferential direction, sothat a circumferential end portion of the oil groove on a front side inthe rotation direction of the crankshaft opens on an end surface 72 onthe front side in the rotation direction of the crankshaft while acircumferential end portion of the oil groove on a rear side in therotation direction of the crankshaft is located in an innercircumferential surface of the main cylinder portion 71.

In this embodiment, the oil groove 41 a has a rectangular shape incross-section. The depth of the oil groove 41 a is constant in thecircumferential direction except the vicinity of the circumferential endportion of the oil groove 41 a on the rear side in the rotationdirection of the crankshaft, and becomes gradually shallow in thevicinity of the circumferential end portion toward the circumferentialend portion on the rear side in the rotation direction of thecrankshaft. Note that in the main cylinder portion 71, the depth of theoil groove 41 a mentioned here refers to a depth from an innercircumferential surface of the main cylinder portion 71 to an oil groovebottom surface, whereas in the crush relief portion 70 and thetransition region 73, the depth of the oil groove 41 a refers to a depthfrom a virtual inner circumferential surface 71 v (see FIG. 7) in thecase in which the crush relief portion 70 and the transition region 73are not formed.

The reason why the oil groove 41 a is configured to open on thecircumferential end surface 72 of the half bearing 41 on the front sidein the rotation direction of the crankshaft is to forward a large amountof oil to an inner circumferential surface of the other half bearing 42to improve the lubrication property. Further, the reason why thecircumferential end portion of the oil groove 41 a on the rear side inthe rotation direction of the crankshaft is configured to be located inthe main cylinder portion 71 is to prevent the oil in the oil groove 41a from flowing out to the relief gap formed by the crush relief portion70 of the half bearing 41 on the rear side in the rotation direction ofthe crankshaft. The length (distance) between the circumferential endportion of the oil groove 41 a on the rear side in the rotationdirection of the crankshaft and the transition region 73 is preferably 1mm or more.

If the circumferential end portion of the oil groove 41 a on the rearside in the rotation direction of the crankshaft opens on thecircumferential end surface 72 or in the crush relief portion 70 of thehalf bearing 41 on the rear side in the rotation direction of thecrankshaft, the bubbles in the oil enter the oil groove 41 a, so thatcavitation erosion may occur in an inner circumferential surface of theoil groove 41 a near the circumferential end portion thereof, or in aninner circumferential surface of the connecting rod bearing 3 due to thebubbles which have been forwarded from the oil groove 41 a to thecrankpin portion 5 side by entering the inside via the inlet opening 6 cfor the lubricating oil path 6 a on the surface of the journal section6.

As is understood from FIG. 3, the oil groove 41 a is disposed in acenter of a width in an axial direction of the half bearing 41. Athrough-port (not illustrated) that penetrates through the half bearing41 in a radial direction is formed in a bottom portion of the oil groove41 a, and the oil is supplied into the oil groove 41 a through thethrough-port from the oil gallery in the wall of the cylinder block. Thewidth of the oil groove 41 a varies depending on the specifications ofthe internal combustion engine, and in the case of a compact internalcombustion engine for a passenger car, for example, is about 4 to 7 mmand a maximum depth (corresponding to the constant depth except theregion of the circumferential end portion of the oil groove 41 a on therear side in the rotation direction of the crankshaft in the case ofEmbodiment 1) of the oil groove 41 a is about 0.5 to 1.5 mm.

Note that the oil groove 41 a is not limited to Embodiment 1, and thewidth and depth of the oil groove may be maximum in the vicinity of thecentral portion of the circumferential length of the oil groove 41 a andmay become small gradually toward the circumferential end portion.

Note that in the invention of the present application, the transitionregion 73 on a front side in the rotational direction of the crankshaftin the lower half bearing 42 which does not have an oil groove, and thetransition region 73 on a rear side in the rotational direction of thecrankshaft in the upper half bearing 41 are essential components,whereas the transition region 73 on a rear side in the lower halfbearing 42 is not an essential component, and the transition region 73on a front side in the rotation direction of the crankshaft in the upperhalf bearing 41 having the oil groove is not an essential component,also.

In Embodiment 1, the half bearings 41 and 42 include the transitionregions 73 on both of the front side and the rear side. UnlikeEmbodiment 1, on the rear side in the rotational direction of thecrankshaft 6, of the half bearing 42, the crush relief portion 70 andthe main cylinder portion 71 may be formed to be directly connected,without forming the transition region 73. Further, without forming thetransition regions 73 in the half bearing 41, the crush relief portions70 and the main cylinder portion 71 may be formed to be directlyconnected. Note that “the transition region 73 on the front side in therotation direction of the crankshaft 6″ means the transition region 73which an optional point on a surface of the journal section 6 which isrotating passes at the second time, out of the transition regions 73located in the vicinities of both ends when attention is paid to the onehalf bearing 41 or 42.

Meanwhile, a crankshaft of an internal combustion engine rotates in onedirection during operation. Accordingly, a person skilled in the artwould be able to recognize which of two crush reliefs adjacent tocircumferential end surfaces of a half bearing corresponds to the“transition region on the front side in the rotation direction of thecrankshaft” taking account of the rotation direction of the crankshaft.Also, the skilled person would be able to design and manufacture themain bearing 4 of the present invention in accordance with thedisclosure of the invention, and to mount this bearing in a bearingdevice which supports the crankshaft rotating in one direction.

If the transition regions 73 are formed on both the front side and therear side in the rotation direction of the crankshaft in the halfbearing 42, commonality of machining steps for the inner circumferentialsurface at both end portions in the circumferential direction of thehalf bearing 42 can be achieved, and if the transition region 73 isformed in the half bearing 41, commonality of machining steps for theinner circumferential surfaces of the half bearing 41 and the halfbearing 42 can be also achieved.

The main cylinder portion 71 has a semi-cylindrical surface thatoccupies most part of the inner circumferential surface of the halfbearing 41 (or 42), and the semi-cylindrical surface forms a mainsliding surface between the semi-cylindrical surface and a mating shaft.The transition region 73 which has a wall thickness gradually decreasingtoward the crush relief portion 70 is provided adjacently to the maincylinder portion 71, as shown in FIGS. 6 and 7. In other words, in thetransition region 73, an inclined curved surface is formed to approachthe mating shaft side from an inner surface of the crush relief portion70 toward an inner surface of the main cylinder portion 71.

The transition region 73 seen from the axial direction of the halfbearing 41 (or 42) is made of an inward protruding curved surface thatprotrudes inward in a radial direction of the half bearing 41 (or 42).Namely, an inclination of the inclined curved surface of the transitionregion 73 to the virtual inner circumferential surface (extended surfaceof the main cylinder portion 71) 71 v of the half bearing 41 seen fromthe axial direction of the half bearing 41 (or 42) becomes the largestat a position connecting to the crush relief portion 70, and becomes thesmallest at a position connecting to the main cylinder portion 71, andthe transition region 73 connects to the main cylinder portion 71smoothly.

Note that the transition region may be formed of a flat surface, and inthat case, a corner portion (a corner edge portion) is formed at aconnection spot of the main cylinder portion 71 and the transitionregion. The corner portion contacts a journal portion surface of thecrankshaft, and damage easily occurs. The transition region is formed bythe inclined curved surface as in the invention of the presentapplication, whereby such a problem hardly arises.

Further, an inner surface shape of the transition region 73 can be sucha shape that a high-pressure oil in the lubricating oil path flows to arelief gap (a gap formed by the inner surface of the transition region73, the inner surface of the crush relief portion 70 and the virtualinner circumferential surface) at a connecting portion of the transitionregion 73 and the main cylinder portion 71. For example, the innersurface shape may include an outward protruding curved surface thatprotrudes to an outer diameter side, or may be a composite curvedsurface in an S-shape having an outward protruding curved surface on aside near to the crush relief portion 70 and an inward protruded curvedsurface on a side far from the crush relief portion 70.

Next, with reference to FIG. 7, specific dimensions of the crush reliefportion 70 and the transition region 73 will be described. FIG. 7 is adevelopment in which the inner circumferential surface of the maincylinder portion 71 is developed to be a flat surface (a straight linein a section).

A depth D1 at the circumferential end surface of a crush relief 70 c maybe similar to the conventional crush relief. Though the depth D1 dependson the specifications of an internal combustion engine, the depth D1 isabout 0.01 to 0.05 mm, for example, in the case of a compact internalcombustion engine bearing for a passenger car. Further, the crush relief70 c is preferably formed from the end portion in the circumferentialdirection of the half bearing to a range of a circumferential angle θ of3° to 15° inclusive toward a central portion side in the circumferentialdirection, for a discharge operation of the high-pressure oil from aninside of the lubricating oil path to the relief gap (see FIGS. 2 and7).

A depth D2 at a position of the crush relief portion 70 connecting tothe transition region 73 can be set at 0.002 to 0.030 mm. If the depthD2 is within the range, (A) even in the region on the upstream side ofthe crush relief, the gap space in which the oil can disperse when theinlet opening 6 c of the oil path 6 a communicates with the transitionregion is formed in the vicinity of the connecting portion of thetransition region 73 and the crush relief portion 70 (FIG. 14B), and (B)the pressure of the oil in the relief gap between a surface of thejournal section 6 of the crankshaft and an inner surface of the crushrelief portion 70 also becomes low in the upstream region. This isbecause when the oil having high pressure in the gap between the maincylinder surface and the journal portion surface advances into therelief gap of the invention of the present application in which a gapcapacity is large (the gap capacity abruptly increases), the pressure ofthe oil is abruptly reduced at the same time. Therefore, the oil thepressure of which is high in a vicinity of the inlet opening 6 c of theinternal oil path 6 a also especially disperses and flows to the reliefgap from a gap between the transition region and the journal surface(FIG. 14A).

Note that when the depth D2 is less than 0.002 mm, the effect ofreducing the pressure of the oil in the relief gap is reduced, andtherefore, the high-pressure oil is difficult to disperse and feed tothe relief gap. Further, when the depth D2 exceeds 0.030 mm, a gap (agap sandwiched by the inner surface of the crush relief portion 70 andthe virtual inner circumferential surface 71 v) of the crush relief 70 cin the end portion in the width direction of the half bearing 41 (or 42)is large, and therefore, a leakage amount of the lubricating oil to theoutside from both end portions in the bearing width direction of thehalf bearing 41 (or 42) becomes large.

A length L2 in the circumferential direction, of the transition region73 according to Embodiment 1 is in a range of 1 to 4 mm, and is morepreferably in a range of 2 to 3 mm.

The crush relief portion 70 according to Embodiment 1 is formed in sucha manner that the depth D1 at the position of the end surface 72 becomesdeeper than the depth D2 at the position connecting to the transitionregion 73 as shown in FIGS. 6 and 7. Here, the depth of the crush relief70 c refers to a distance from the virtual inner circumferential surface71 v which is obtained by extending the inner circumferential surface ofthe main cylinder portion 71 over the crush relief portion 70 to thesurface of the crush relief portion 70.

Furthermore, the crush relief 70 c according to the present embodimentis formed by an outward protruding curved surface in an outwardprotruding shape in the radial direction of each of the half bearings 41and 42. Namely, an inclination of the inner surface of the crush reliefportion 70 with respect to the virtual inner circumferential surface 71v of the half bearing when seen from the axial direction of the halfbearing is maximum at the position connecting to the transition region73, is minimum at the position of the end surface 72, and issubstantially parallel with the virtual inner circumferential surface 71v.

Note that shapes of the main cylinder portion 71, the crush reliefportion 70 and the transition region 73 that are described above aremeasurable by an ordinary shape measuring instrument, for example, aroundness measuring instrument. Namely, in a state in which the bearingis assembled into the actual bearing housing section at the cylinderblock lower part, or the housing similar thereto, the shape of the innersurface of the bearing can be measured continuously in thecircumferential direction.

In the crush relief portions 70, a plurality of crush relief grooves 74and 75 are formed throughout an entire length in the circumferentialdirection of the inner circumferential surfaces of the crush reliefportions 70 to extend parallel with the circumferential direction of thebearing, as shown in FIGS. 3 and 4. The plurality of crush reliefgrooves 74 and 75 are disposed parallel with one another in the widthdirection of the half bearings 41 and 42, and are formed throughout theentire width. Accordingly, a flat region is not present on the innercircumferential surfaces of the crush relief portions (except for aformation range of the oil groove 41 a of the half bearing 41). Further,all of the plurality of crush relief grooves 74 and 75 are formed intothe same groove widths and groove depths, and are also formed into thesame groove widths and groove depths throughout the entire length in thecircumferential direction of the circumferential surface of the crushrelief portion 70.

Describing in more detail, the crush relief groove 74 is formed into acircular-arc shape (a shape in which a circular-arc portion is on a backside) with a predetermined groove width WG and a predetermined groovedepth DG, as shown in FIG. 8. In other words, the individual crushrelief grooves 74 are cut grooves each in a U-shape, provided inparallel at constant intervals (WG) in the width direction, and form asection in a saw-tooth shape or a shallow comb shape as a whole. Here,the groove width WG refers to the distance in the width direction of thehalf bearings 41 and 42 between apexes of adjacent peak portions, andthe groove depth DG refers to a distance in a direction perpendicular tothe inner circumferential surface from the apex to a bottom point of avalley portion. More specifically, the crush relief groove 74 preferablyhas the groove width WG of 0.05 to 0.5 mm, and the groove depth DG of 1to 20 μm.

Here, the crush relief portions 70 are configured so that the pluralityof crush relief grooves 74, 75 are formed on the inner circumferentialsurfaces thereof, however, the crush relief grooves 74, 75 are notformed continuously in the transition regions 73 as shown in FIG. 7, andthus a boundary between the crush relief 70 and the transition region 73is clear.

According to the invention of the present application, as shown in FIGS.13A and 14A, the plurality of crush relief grooves 75 are formedthroughout the entire length in the circumferential direction of theinner circumferential surface of the crush relief portion 70 to extendparallel with the circumferential direction of the bearing. When amongthe crush relief grooves 75 of the half bearing 42 on the lower side ofFIG. 13A, for example, the crush relief grooves 75 on the right side ofthe page from the central portion in the axial direction of the halfbearing 42 and the crush relief grooves on the left side of the page areinclined toward the central portion (the oil groove 41 a of the halfbearing 41 on the upper side) in the axial direction of the half bearing42 (inclined with respect to the circumferential direction of thebearing), instead of the circumferential direction, unlike the inventionof the present application, a vacancy (an bubble) generated in therelief gap is fed toward the central portion (the oil groove 41 a side)in the axial direction of the half bearing 41 on the upper side, andtherefore, is difficult to discharge to an outside of the bearing.Further, for example, when among the crush relief grooves 75 of the halfbearing 42 on the lower side in FIG. 13A, the crush relief grooves 75 onthe right side on the page from the central portion in the axialdirection of the half bearing 42 and the crush relief grooves on theleft side on the page are inclined toward the end portion in the axialdirection of the half bearing 42, the leakage amount of the oil to theoutside from the half bearing 41 becomes large.

Furthermore, as shown in FIGS. 3, 4, 6, 7 and 9, in the crush reliefportions 70, inclined surfaces 76 that continuously extend in the axialdirection of the half bearings 41 and 42 are formed at inner end edgesin the circumferential direction of the half bearings 41 and 42. Namely,an axial groove 77 is formed along inner edges of the circumferentialend surfaces 72 that abut on each other, and throughout the entirelength of the width in the axial direction of the main bearing, in astate in which the pair of half bearings 41 and 42 are combined into acylindrical shape. Note that unlike Embodiment 1, the inclined surface76 may be formed on only one end surface in the circumferentialdirection out of the two circumferential end surfaces 72 which abut oneach other. In that case, when the pair of half bearings 41 and 42 iscombined into the cylindrical shape, the inclined surface 76 forms theaxial groove 77 in cooperation with the other circumferential endsurface 72.

More specifically, the axial groove 77 preferably has a groove width WJof 0.3 to 2 mm in the circumferential direction in the combined state,and a groove depth DJ in the radial direction of 0.1 to 1 mm. The axialgroove 77 to be an exhaust path for the oil including vacancies(bubbles) can be in any size as long as passage of the oil includingvacancies (bubbles) is enabled, and is not affected by the size of thebearing. Note that in FIG. 9, the groove with a V-shaped section isshown as the axial groove 77, but the sectional shape is not limitedthereto as long as passage of the oil including vacancies (bubbles) isenabled.

The axial groove 77 is formed to be deeper than the crush relief groove75. Therefore, an opening of the crush relief groove 75 at the endportion in the circumferential direction opens to an inner surface (theinclined surface 76) of the axial groove 77. Therefore, the oilincluding vacancies (bubbles) which flows by being guided by the innersurface recessed portion of the crush relief groove 74 directly advancesinto the axial groove 77, and therefore, an oil flow to the axialdirection is easily formed in the axial groove 77. Accordingly, the oilincluding vacancies (bubbles) that advances into the axial groove 77together with the lubricating oil is easily discharged outside thebearing.

The invention of the present application has an object to restraincavitation erosion in the inner circumferential surface of the crushrelief portion 70 by dispersing an oil flowing out of the inlet opening6 c and thereby preventing the high-pressure oil from concentratedlyflowing to the region near the end portion on the central portion sidein the circumferential direction of the crush relief 70 c on the rearside in the rotation direction of the other half bearing 41, over whichregion the inlet opening 6 c on the surface of the journal section 6passes. However, in order not to cause the high-pressure oil to flow tothe half bearing 41 more, the crush relief grooves 74 and 75 arepreferably arranged as follows.

In the crush relief portion 70 of the other half bearing 41 which ispaired with the one half bearing 42, the plurality of crush reliefgrooves 74 that continue in the circumferential direction are provided.In the present embodiment, as shown in FIGS. 10 and 12, the plurality ofcrush relief grooves 75 of the one half bearing 42 of the presentembodiment are each displaced by a half of the groove width WG in thewidth direction, with respect to the plurality of crush relief grooves74 of the other half bearing 41. Namely, in the butting portions of thecircumferential end surfaces of the pair of half bearings 41 and 42,that is, a connecting position of the one crush relief groove 74 and theother crush relief groove 75 (actually are not directly connectedbecause the axial groove 77 is present), the valley portion (an openingin a recessed shape of the crush relief groove) of the one crush reliefgroove 74 is disposed to correspond to the peak portion (the protrudedshape formed between the two adjacent circumferential grooves 74) of theother crush relief groove 75.

Accordingly, since the vacancies (bubbles) generated in the oil receiveresistance in the connecting position of the crush relief groove 74 andthe crush relief groove 75, the vacancies (bubbles) that flow in thecrush relief groove 75 of the one half bearing 42 hardly advance intothe crush relief groove 74 of the other half bearing 41, and are easilydischarged to the outside of the bearing by the oil flow that flows tothe end portion side in the bearing width direction in the axial groove77 at the same time. Note that the oil also receives resistance in theconnecting position of the crush relief groove 74 and the crush reliefgroove 75, and also flows from the crush relief groove 75 to the crushrelief groove 74.

Embodiment 2

In Embodiment 2, unlike the one half bearing 41 of Embodiment 1, the oilgroove 41 a is formed in such a manner that its depth from the maincylinder surface is maximum at the circumferential end surface 72 of thehalf bearing 41 on the front side in the rotation direction of thecrankshaft, and becomes gradually smaller toward the circumferential endportion on the rear side in the rotation direction of the crankshaft, asshown in FIG. 11. Note that the depth of the oil groove 41 a at thecircumferential end surface 72 on the front side in the rotationdirection of the crankshaft refers to a depth to a bottom surface of theoil groove 41 a from a virtual main cylinder surface 71 obtained in thecase that the crush relief portion 70 and the inclined surface 76 arenot formed. The circumferential end portion of the oil groove 41 a onthe rear side in the rotation direction of the crankshaft is positionedin the inner circumferential surface of the main cylinder portion 71also. The other configuration is the same as the configuration of thehalf bearing 41 of Embodiment 1.

In Embodiment 2, as shown in FIGS. 10 and 12, in the crush reliefportion 70 of the other half bearing 42 which is paired with the onehalf bearing 41, a plurality of crush relief grooves 75 extending in thecircumferential direction are provided. The plurality of crush reliefgrooves 74 of the one half bearing 41 of the present embodiment are eachdisplaced by a half of the groove width WG in the width direction withrespect to each of the plurality of crush relief grooves 75 of the otherhalf bearing 42.

Embodiment 2 has the operative effect in common with Embodiment 1, andfurther has an effect of hardly causing the problem that cavitationerosion occurs on a sliding surface of the connecting rod bearing 3 atthe crankpin portion 5 by the oil forwarded from the oil groove 41 a ofthe half bearing 41 to the crankpin portion 5 side.

More specifically, because the oil supplied into the oil groove 41 aflows in the oil groove 41 a toward the front side in the rotationdirection of the crankshaft by accompanying the surface of the journalsection 6 of the crankshaft, the oil is pressurized near thecircumferential end portion of the oil groove 41 a on the front side inthe rotation direction of the crankshaft and increases in pressure.Accordingly, if the oil groove 41 a has a constant depth in thecircumferential direction (i.e. a cross sectional area of the oil grooveis constant in the circumferential direction), or a depth which becomesgradually small toward the circumferential end portion on the front sidein the rotation direction of the crankshaft (i.e. a cross sectional areaof the oil groove decreases toward the front side in the rotationdirection of the crankshaft), the pressure of the oil may becomeexcessively high near the circumferential end portion of the oil groove41 a on the front side in the rotation direction of the crankshaft.Consequently, when the inlet opening 6 c of the lubricating oil path 6 aon the surface of the journal section 6 passes near the circumferentialend portion of the oil groove 41 a on the front side in the rotationdirection of the crankshaft, the oil under high pressure is forwarded tothe crankpin portion 5 side. Then, when the oil flows out in the gapbetween the inner circumferential surface of the connecting rod bearing3 and the surface of the crankpin 5, the pressure of the oil rapidlyreduces, and a vacancy (a bubble) may be generated in the oil. By animpact force generated when the vacancy (bubble) collapses, cavitationerosion may occur on the inner circumferential surface of the connectingrod bearing 3.

On the contrary, when the oil groove 41 a is configured so that itsdepth becomes large toward the front side in the rotation direction ofthe crankshaft like Embodiment 2, the cross sectional area of the oilgroove 41 a becomes large toward the front side in the rotationdirection of the crankshaft, and therefore the pressure of the oil doesnot become excessively high near the circumferential end portion of theoil groove 41 a on the front side in the rotation direction of thecrankshaft, so that occurrence of the cavitation erosion on the slidingsurface of the connecting rod bearing 3 can be restrained.

While each of Embodiment 1 and Embodiment 2 shows the example in whichthe plurality of crush relief grooves 74 of the one half bearing 41 areeach displaced by a half of the groove width WG in the width directionwith respect to the plurality of crush relief grooves 75 of the otherhalf bearing 42, the invention of the present application is not limitedthereto. The plurality of crush relief grooves 74 may be displacedwithin a range that exceeds zero and is less than the groove width WG inthe width direction, with respect to the plurality of crush reliefgrooves 75 of the other half bearing 42. In other words, the crushrelief groove 74 on one side and the crush relief groove 75 on the otherside can be disposed by the positions of the respective central portionsin the groove widths are displaced in the width direction in a rangewhich exceeds at least zero and is less than the groove width WG at themaximum in the connecting position. Further, more preferably, the crushrelief groove 74 on the one side and the crush relief groove 75 on theother side are disposed in such a manner that the respective positionsof the central portions in the groove widths are displaced in the widthdirection of the half bearing 41 in a range of at least 10% of thegroove width WG to 50% inclusive of the groove width WG at the maximumin the connecting position. However, the crush relief groove 74 and thecrush relief groove 75 may conform to each other, though dischargeperformance for vacancies is slightly low.

While the embodiments of the invention of the present application aredescribed in detail with reference to the drawing, the specificconfiguration is not limited to the embodiments, and design changes tothe extent without departing from the gist of the invention of thepresent application are included in the invention of the presentapplication.

For example, in each of the embodiments, the case in which the pluralityof crush relief grooves 75 are provided at only the crush relief portion70 is described, but a plurality of circumferential grooves may beprovided in the main cylinder surface. Further, a plurality ofcircumferential grooves may be provided in the transition region 73.However, the circumferential grooves formed in the main cylinder surfaceand the transition region 73 should have a smaller groove depth than thecrush relief grooves 74, 75, and the crush relief grooves 74, 75 shouldnot be formed so as to extend up to the transition region 73 and themain cylinder surface. Further, the oil groove 41 a has a rectangularshape in cross-section in the embodiments, but may have an inversedtrapezoidal shape in cross-section. Furthermore, a region where thebearing wall thickness decreases (a crowning portion) may be provided onthe inner circumferential surface sides of both the end portions in theaxial direction of the half bearings 41 and 42. Further, although theembodiments show the example in which the main bearing 4 supports thecrankshaft with two inlet openings 6 c for the inner oil path 6 a on thesurface of the journal section 6, the present invention is not limitedto this, and may be applied to a main bearing 4 which supports acrankshaft with one opening 6 c, or with three or more openings 6 c fora lubricating oil path 6 a on a surface of a journal section 6.

1. A main bearing for rotatably supporting a journal section of acrankshaft of an internal combustion engine, the journal sectioncomprising a cylindrical body portion, a lubricating oil path extendingto penetrate the cylindrical body portion, and at least one inletopening of the lubricating oil path that is formed on an outerperipheral surface of the cylindrical body portion, wherein the mainbearing comprises first and second half bearings which are combined intoa cylindrical shape by butting respective circumferential end surfacesthereof, the first and second half bearings are configured so as to formtogether an axial groove extending through an entire length of the mainbearing in an axial direction on an inner circumferential side of eachbutting portion when the first and second half bearings are combined,each half bearing comprises a main cylinder portion including acircumferential central portion of the half bearing, and crush reliefportions which are formed over the entire length in the axial directionat both circumferential end portions of the half bearing so that a wallthickness of the crush relief portion is thinner than that of the maincylinder portion, and each crush relief portion extending from thecircumferential end surface toward the circumferential central portionof the half bearing with a center angle not less than 3° but not morethan 15°, a plurality of crush relief grooves extending in thecircumferential direction over an entire length of the crush reliefportion are formed in each crush relief portion so as to communicatewith the axial groove, an oil groove is formed only on an innercircumferential surface of the first one of the first and second halfbearings to extend in the circumferential direction, a circumferentialend portion of the oil groove on a front side of a rotation direction ofthe crankshaft opening on the circumferential end surface of the firsthalf bearing on the front side of the rotation direction, acircumferential end portion of the oil groove on a rear side of therotation direction of the crankshaft being positioned in the maincylinder portion of the first half bearing, the first half bearingfurther comprises a transition region formed at least between the crushrelief portion on the rear side in the rotation direction of thecrankshaft and the main cylinder portion so that a wall thickness of thetransition region becomes thinner toward the crush relief portion fromthe main cylinder portion, the second half bearing further comprises atransition region formed at least between the crush relief portion onthe front side in the rotation direction of the crankshaft and the maincylinder portion so that a wall thickness of the transition regionbecomes thinner toward the crush relief portion from the main cylinderportion, and each of the transition regions comprises an inwardprotruding curved surface in a protruding shape which protrudes inwardin a radial direction, seen from the axial direction of the halfbearing.
 2. The main bearing according to claim 1, wherein each crushrelief portion connecting with the transition region has a depth of0.002 mm to 0.030 mm in a radial direction at the connecting position.3. The main bearing according to claim 1, wherein each transition regionhas a length of 1 mm to 4 mm in the circumferential direction.
 4. Themain bearing according to claim 1, wherein each crush relief groove hasa depth of 1 μm to 20 μm in the radial direction, and a width of 0.05 mmto 0.5 mm in the axial direction.
 5. The main bearing according to claim1, wherein when the first and second half bearings are combined, therespective crush relief grooves formed in the crush relief portions ofthe first half bearings are adapted to be displaced in the axialdirection with respect to the respective crush relief grooves formed inthe crush relief portions of the second half bearing by an amountexceeding zero at a minimum and less than the width of the crush reliefgroove at a maximum.
 6. The main bearing according to claim 1, whereineach axial groove has a depth of 0.1 mm to 1 mm in the radial direction,and a width of 0.3 mm to 2.0 mm in the circumferential direction.
 7. Themain bearing according to claim 1, wherein each transition region hasthe inward protruding curved surface on a side far from the crush reliefportion, and has an outward protruding curved surface in a protrudingshape protruding outward in the radial direction on a side near thecrush relief portion.
 8. The main bearing according to claim 1, whereinthe depth of the oil groove is maximum at the circumferential endsurface of the first half bearing on the front side of the rotationdirection, and becomes smaller toward the circumferential end portion ofthe oil groove on the rear side of the rotation direction.